1. Field of the Invention
This invention relates to processes for making vinyl caprolactam (VCL)-based polymers, and, more particularly, to a suspension polymerization process for making such polymers in water without requiring the addition of protective colloids, and which are obtained thereby as substantially odor-free polymers, without residual monomers, and in an environmentally friendly solvent.
2. Description of the Prior Art
J. Kroker et al, in U.S. Pat. No. 5,739,195, described a process for preparing an aqueous solution of 10-60% polyvinyl caprolactam (PVCL) homopolymer at a temperature above its cloud point in the presence of 0.1-20% by weight based upon vinyl caprolactam (VCL) monomer of a water-soluble synthetic polymeric protective colloid. Aqueous polyvinyl caprolactam homopolymer made with a protective colloid present in the starting materials was homogeneous, whereas protective colloid free systems were inhomogeneous, which were not readily dilutable with water except stirring for a prolonged period of time. Addition of an emulsifier to the starting material also formed an appreciable portion of PVCL polymer remained attached to the stirrer element.
Accordingly, it is an object of this invention to provide a process for making VCL-based polymers in water without requiring addition of a water-soluble synthetic protective colloid in the reaction mixture.
Another object herein is to provide a process of making VCL-based copolymers and terpolymers by suspension polymerization in which the monomers are fed into the reaction vessel at a predetermined feeding schedule.
Still another object herein is to provide an aqueous solution of VCL-based polymers which are substantially odor-free, monomer-free and uncontaminated by the presence therein of protective colloids.
A feature of the invention is the provision of an aqueous suspension polymerization process for making VCL-based copolymers or terpolymers wherein a suitable dispersing agent for the copolymer product is generated in-situ during the polymerization.
These and other objects and features of the invention will be made apparent from the following description thereof.
What is described herein is an aqueous suspension polymerization process for making VCL-based polymers without an added protective colloid, in which the monomers are introduced into the reaction vessel at a predetermined feeding schedule, and wherein the dispersing agent to keep the copolymer product in a stirrable state during the polymerization is generated in situ during the course of the polymerization. In this invention, accordingly, the polymerization process proceeds smoothly to form a uniform suspension of fine polymer particles in water at a temperature above the cloud point of the polymer without developing large lumps of polymer material during polymerization.
The product of this process is an odor-free, monomer-free, aqueous solution of the desired VCL-based polymer uncontaminated by a protective colloid.
The process is adaptable to any VCL-based polymers, which are made by copolymerizing VCL monomer with one or more substantially water-soluble monomers. Examples of representative copolymers, are copolymers of VCL and vinyl pyrrolidone (VP); copolymers of VCL and N-vinyl-N-methylacetamide (VIMA); terpolymers of VCL/VP/M3, where M3 is a linear, acylic N-vinylamide monomer which is N-vinyl formamide, N-vinyl acetamide or N-vinyl-N-methylacetamide (VIMA), in predetermined proportions of each monomers, preferably at least 40% by wt. VCL, most preferably at least 50% by wt., the rest being VP and/or a linear, acylic N-vinylamide; and mixtures thereof.
The product can be used to provide completely alcohol-free, hair care compositions, e.g., 0% VOC hair fixatives and hair conditioners, gas hydrate inhibitors and ink-jet printing media.
The polymerization process of the invention is carried out at a temperature of at least 15xc2x0 C., preferably 35xc2x0 C., above the cloud point of the polymer, as a suspension polymerization. In this protective colloid-free system, the monomers are fed into the reaction vessel at a predetermined feeding schedule to generate a polymer product in-situ at an early stage of the reaction as the dispersing agent to maintain the copolymer particles suspended in water during the polymerization. Accordingly, no added protective colloid is necessary in this process. The polymer product thus is a fine dispersion of polymer particles in water before cooling, without any polymer build-up on the agitator shaft and/or reactor wall, which causes agitation problems and a prolonged period of time to re-dissolve the polymer in water.
In a typical run, about 2-25%, preferably 3-15%, of the total amount of VP, or a substantially water-soluble monomer (M3) or VP/M3, with initiator is fed into water at the reaction temperature over 30 minutes, followed by metering in the remaining monomer pre-mix with initiator over 1-4 hours. Alternatively, the initiator can be fed separately into the reaction vessel. After holding the reaction mixture for one hour, 2-4 additional booster shots of initiators are added to react out any residual monomer to the desired low level. At the end of the reaction, the batch is cooled to ambient conditions to form a clear, viscous polymer solution.
As described, the VCL-based copolymers of the present invention, copolymers are made by copolymerizing VCL monomer with one or more substantially water-soluble monomers in predetermined proportions of each monomer. Examples of representative water-soluble comonomers, but not limited to, are vinyl amides such as vinylpyrrolidone, N-vinylformamide, N-vinylacetamide and N-vinyl-N-methylacetamide.
Usually the polymerization processes in water is performed at a temperature between 50xc2x0 to 100xc2x0 C. under nitrogen atmosphere, although polymerization can also be carried out at a temperature above 100xc2x0 C. under pressure, or at a temperature below 50xc2x0 C. using redox initiators. Suitable polymerization initiators typically have a half-life of 1-5 hours at a given polymerization temperature. Representative polymerization initiators include azo compounds such as 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile) (VAZO-52), 2,2xe2x80x2-azobis(isobutyronitrile) (VAZO-64), 2,2xe2x80x2-azobis(methylbutyronitrile) (VAZO-67) and 1,1xe2x80x2-azobis(cyanocyclohexane) (VAZO-88, du Pont); peroxyesters such as t-butyl peroxypivalate (Lupersol 11M75), t-amyl peroxypivalate (Lupersol 554M75) and t-amyl peroxy-2-ethylhexanote (Lupersol 575, Elf Atochem); peroxydicarbonates such as di-(2-ethylhexyl) peroxydicarbonate (Lupersol 223, Elf Atochem) and di-(4-t-butylcyclohexyl) peroxydicarbonate (Perkadox 16S, Akzo Nobel). During the residual monomer reduction period, a second polymerization initiator, if needed, can be used to speed up the polymerization cycle. The residual monomers can be eliminated by treatment with hydrogen peroxide thereby to minimize odor in the product.
The process of the invention enables the synthesis of VCL-based polymers directly in water. Water is an environmentally friendly solvent and is preferred in many end uses, for example, hair care formulations such as hairsprays, mousses, styling gel, etc., gas hydrate inhibition, ink jet printing, and the like.
The term polymer, copolymer or terpolymer, as used herein, refers to VCL-based polymers with one or more monomers, and allows for copolymers, terpolymers, tetrapolymers, etc. as desired. Suitably such VCL-based polymers should contain at least about 40% VCL, and preferably 50% or more, by weight, in the composition.
The invention will now be described in more detail with reference to the following examples.